One known arrangement for a dental implant involves an implant portion, or artificial root, that is received in a hole prepared in alveolar bone, and an abutment, or prosthesis support, that is securable to the implant portion and that extends beyond the gingival tissue to support a tooth prosthesis. The implant portion and the abutment are constructed as separate components that are secured together by means of a screw passed through the abutment and received within a threaded bore in the implant portion.
In a first surgical procedure, an incision is made in the gingival tissue to expose the alveolar bone. Following any dressing of the surface of the bone that may be necessary, a hole that is complementary in shape to the implant portion is drilled in the bone and the implant portion is inserted. A healing cap or screw is attached to the implant portion to occlude the threaded bore, and the gingival tissue is stitched closed over the implant portion to await osseointegration.
In a subsequent second surgical procedure, following osseointegration of the implant portion, the gingival tissue is again opened to expose the implant portion. The healing cap or screw is removed and replaced with a second healing cap having an outer surface corresponding in shape below the gum-line to that of the abutment, but protruding slightly above the gingival tissue. The gingival tissue surrounding the second healing cap is sutured thereabout to await healing in conformity to the outer surface of the second healing cap.
After the gingival tissue has healed, the second healing cap is removed and replaced with a permanent abutment that is secured to the implant. The abutment can be configured to support a single-tooth prosthesis fashioned thereon or to support a bridge structure carrying multiple tooth prostheses.
A common clinical problem associated with dental implants is loss of supporting bone at the coronal aspect of the implant. Such loss of bone can be caused by, among other things, infectious etiologies similar to those encountered in periodontal diseases of natural teeth. The association of periodontal pathogenic organisms with the loss of supporting alveolar bone highlights the need for scrupulous oral hygiene on the part of the patient and for the ability of a clinician to adequately prevent disease and to treat diseased implant sites. A smooth surface at the coronal end of a dental implant is more easily cleaned of plaque, pathogenic organisms, and endotoxins than is a rough surface that has crevices that cannot be reached readily by mechanical devices such as brushes. A smooth surface at the coronal end of an implant also facilitates increased accuracy of fit at the interface between the implant and the attached abutment, an important consideration since gaps between these components can harbor pathogenic accumulations, potentially leading to adverse clinical conditions. Consequently, dental implants with a smooth surface in the coronal region are commonly used in clinical practice.
Bone tissue reacts differently to metal surfaces with differing surface characteristics. Buser et al. (J Biomed Mater Res 25: 889-902, 1991) implanted cylindrical titanium implants having different surface characteristics in miniature pigs. They reported that the percentage of implant surface in direct contact with bone varied directly with increasing roughness of the titanium surface. It has also been observed by others that bone often does not attach to the smooth surface in the coronal region of dental implants. Rather, remodeling of the bone occurs such that the coronal attachment of bone is lowered to the first roughened or textured surface encountered.
To enhance osseointegration of dental implants, it has been proposed to provide a porous surface on the bone-engaging portion of the implant to permit ingrowth of bone into the surface of the implant. Such a porous surface can be provided on a metal implant by a coating of sintered metal powder, beads, or wire mesh, for example. Concerns have been expressed by some persons, however, that exposure of the porous surface of a dental implant to the oral cavity can result in apical migration of bacteria from the oral cavity through the pores of the porous surface, leading to infection of the bone and consequent loss of bony support for the implant. With that concern in mind, a porous coated dental implant is shown in U.S. Pat. No. 5,344,457, to Pilliar et al. wherein the implant includes a lower bone-engaging region coated with a porous surface into which bone may grow, and an upper bone-engaging region coated with a non-porous, relatively smooth, bioreactive surface (such as hydroxylapatite) to which bone can bond directly. The presence of bone in apposition to the implant surface above the level of the porous surface is said to afford protection of the porous surface from the migration of pathogens from the oral cavity.
It would be desirable to have an implant that offers optimum anchoring in bone by ingrowth of bone into a porous surface, a coronal surface designed for optimum hygiene, and protection of the porous surface from the oral cavity not afforded by smooth coronal surfaces. This and other desirable advantages are provided by the present invention.